NORA Manufacturing Sector Strategic Goals
927ZJGD - Calibration Methods for Direct Reading Aerosol MonitorsStart Date: 10/1/2009
End Date: 9/30/2012
Principal Investigator (PI)Name: Terri Pearce
Funded By: NIOSH
Primary Goal Addressed5.0
Secondary Goal AddressedNone
Attributed to Manufacturing50%
Industrial hygienists use direct-reading aerosol monitors (DRAMs) for decision making about exposure differences between workers or job tasks. However, a recently-completed NIOSH study challenging four different DRAMs with a standard test dust aerosol found that not only did DRAMs of different types provide results more than 25 percent different than a reference sampler but that individual monitors of a specific type also differed in the comparability of their results. The monitors used in that study were intentionally not calibrated to the challenge aerosol in order to evaluate how different the results would be when the dust of interest was unknown or when DRAMs are used for referential measurements (e.g., high versus low aerosol generation). Most manufacturers recommend calibrating to the dust of interest although they do not often provide specifics about how to do so. The NIOSH Manual of Analytical Methods Chapter G provides guidance for using aerosol photometers and mentions calibrating to the aerosol of interest without providing specifics on how such calibration should be accomplished. This proposed research seeks to develop specific methodology for calibrating DRAMs and to communicate the findings to the industrial hygiene community including the provision of updates to existing NIOSH guidance.
This laboratory project will develop methods for calibrating DRAMs to measure dusts that are commonly encountered in workplaces. The goal is to provide information that can be used to update and extend existing NIOSH guidance. The project will evaluate the performance of two commercially-available DRAMs, a nephelometer (ThermoElectron pDR-1500™) and a laser spectrometer (Grimm Personal Dust Monitor™) chosen because each contains an internal filter. The challenge dust will be Arizona Road Dust (ARD), chosen because it is considered a standard test dust, is used by some manufacturers for DRAM calibration, and is composed primarily of silica, which is commonly encountered in the workplace as an aerosol. Polydisperse ARD aerosols will be generated into an exposure chamber at specific concentrations and sampled in parallel by the DRAMs and filter cassettes (NIOSH Method 0500). The filters retrieved from the DRAMs and the cassettes will be weighed in-house to determine the comparability of the DRAM-measured mass concentration, the DRAM filter weight, and the reference sampler weight. The comparison will be conducted both with and without calibrating the DRAM-measured concentration according to the manufacturer guidance. The evaluation will be repeated by generating the ARD in only the respirable size fraction to determine the detection efficiency of the monitors across particle size versus the concentrations measured using cyclone samplers (NIOSH Method 0600). In Phase II, the DRAMs will be re-evaluated using a 50/50 mixture of ARD spiked with titanium dioxide. The dust will be generated in both polydisperse and size-fractionated form. After weighing in-house, the filters from the reference sampler and the DRAMs will be sent to the NIOSH contract laboratory for both silica and TiO2 determination to evaluate the consistency of the proportions between the bulk material and the sampled aerosol. The DRAM performance will be determined according to NIOSH Guidelines for Air Sampling and Analytical Method Development and Evaluation methods. Comparison of the mean recorded levels for a given aerosol will be compared to concentrations measured using NIOSH Methods 0500 (total) or 0600 (respirable). Methods for making the comparability determinations between the DRAMs and the reference method will be reported in the peer-reviewed literature and presented for updates to NIOSH guidance.
Objective: Provide information to be disseminated to the industrial hygiene community through the NIOSH Manual of Analytical Methods (NMAM) by updating the guidance in Chapter G - Aerosol Photometers for Respirable Dust Measurements.
The Exposure Assessment Cross-sector has specified that NIOSH “Produce guidance documents for the development, evaluation, selection, and use of direct reading methods and instruments, data loggers, or diffusive sampling monitoring methods, including information for educating and training purchasers and users to better understand the operation and operating principles; capabilities and limitations; and data interpretation aspects of specific methods”. In the case of aerosol exposure assessment, direct-reading aerosol monitors are being used by industrial hygienists for decision making about exposure differences between workers or job tasks. However, a recently-completed NIOSH study challenging four different aerosol monitors with a standard test dust found that not only did different monitor types provide results more than 25 percent different than a reference sampler but that individual monitors of a specific type also differed in the comparability of their results. The monitors used in that study were intentionally not calibrated to the challenge aerosol in order to evaluate how different the results would be when the dust of interest was unknown or when the monitors are used for referential measurements (e.g., high versus low aerosol generation).